Typically it does involve some kind of trauma during childhood. Some kind of deprivation, some kind of neglect, some kind of abandonment. What we refer to psychoanalytically as severe narcissistic wounding, where the child’s basic needs for recognition of who they are and acceptance of who they are - and for love – are not met.

For example, Diamond says, you take someone who had a traumatic childhood like

Charles Manson; he had an alcoholic mother who abandoned him

several times and tried to sell him. He spent time living in the streets. Eventually a person like that can develop a rage around how they’re being treated.

In my opinion, it is this anger that festers over time, that turns into resentment, that turns into embitterment, that turns into rage. It is this rage that underlies what we call — what you’re referring to – as evil, or evil behavior or evil deeds. That's really, to me, the driving force in violence.

Okay … but what about someone who didn’t have an extremely

neglectful childhood. If Juran van der Sloot turns out to be guilty, he would seem to go against that idea. He came from an intact family with professionally successful parents. Diamond said:

This idea of narcissistic wounding is still there. It’s still possible because narcissistic wounding is something that can be much more subtle. In other words, the trauma is more subtle, so if a child is in certain ways not accepted for who he is in a family, is put down, is criticized constantly or is not given enough attention or affection. Then this is a form of narcissistic wounding. And this can lead a lot of anger. And rage.

But lots of people feel similar emotions at some point during

their upbringing and don't grow up to be violent murderers. Diamond:

There are a lot of mental health professionals who would tell you that there’s some kind of a biological or genetic predisposition to this kind of behavior, or developing this kind of personality disorder – I tend to doubt that. I think that the fact is that what we call psychopaths or antisocial personality disorder or sociopaths — which are really all the same thing – are not born, but are made. The thing is, different individuals do have different temperaments certainly, and so there can be temperamental differences. And these differences influence how a child or an adolescent deals with these kinds of situations and how they cope with it.

Diamond says kids need boundaries and limit-setting to develop a sense of morality and to learn appropriate behavior. Without that attention or discipline, kids may get the message that they aren't worth the effort in the first place. And that can play a role in developing what Diamond refers to as "psychopathic narcissism," or narcissism gone to an extreme. He cites O.J. Simpson as an example.

It's what happens when the child doesn't get certain needs met when they're growing up or is overindulged in certain ways. It's feeling like they have the right to intrude on other people's lives, to manipulate other people — it's all about them. And they tend to not have much of a sense of conscience or guilt about what they do because they're so self-serving.

In other words, the ability to commit acts of evil doesn't just come out of nowhere …

Behavior doesn't just happen out of the clear blue. There's always some prelude to it.

To get Diamond's views on the Juran van der Sloot specifically, check out his post on Evil Deeds. And if you want even more info on the genesis of evil, he's also written a book on it.